Method and system for avoiding damage to derricks by preventing overload conditions

ABSTRACT

The invention involves a method of operating a hydraulic actuated derrick or crane while lifting or pulling anchored objects by winching with the boom resting on a stiff leg and the derrick control in the boom down position. A pressure relief valve and bypass line is provided in the hydraulic circuit to function in lieu of and in conjunction with possible downward movement of the boom thus avoiding damage to the derrick or boom.

United States Patent Charles J. Sauber Sauber Road, Virgil, Ill. 60182751,901

Aug. 12, 1968 Mar. 30, 1971 lnventor Appl. No. Filed Patented METHOD ANDSYSTEM FOR AVOIDING DAMAGE TO DERRICKS BY PREVENTING OVERLOAD CONDITIONS2 Claims, 3 Drawing Figs.

U.S. Cl 212/35, 212/144, 212/145 Int. Cl B66c 23/06 Field ofSearch212/35, 39, 8.145; 60/52, 53

References Cited UNITED STATES PATENTS 2,517,434 8/1950 Humpal 212/352,581,087 1/1952 Eakin 212/8 3,370,601 2/1968 Nevulis 212/35 FOREIGNPATENTS 526,135 12/1954 Italy 212/145 Primary Examiner-Harvey C. HornsbyAttorney-Nicholas M. Esser ABSTRACT: The invention involves a method ofoperating a hydraulic actuated derrick or crane while lifting or pullinganchored objects by winching with the boom resting on a stiff leg andthe derrick control in the boom down position. A pressure relief valveand bypass line is provided in the hydraulic circuit to function in lieuof and in conjunction with possible downward movement of the boom thusavoiding damage to the derrick or boom.

Patented March 30, 1971 l I I Inventor Charles J. Sauber METHOD ANDSYSTEM FOR AVOIDING DAMAGE TO DERRICKS BY PREVENTING 'OVERLOADCONDITIONS The present invention relates to a method of utilizing aderrick or crank boom mounted on a motor vehicle, which derrick or craneis hydraulically actuated for lift and lowering, and which is alsoprovided with an independently operated winch and cable. Moreparticularly, the invention also relates to an improvement in thehydraulic circuitry and associated apparatus for bypassing hydraulicfluid when the pressure condition reaches a preselected pressure shortof that which would cause damage to the crane boom or derrick if notrelieved. The improved system is particularly advantageous in preventingdamage to the derrick or crane boom held in a near horizontal positionwhile the associated winch is effecting a pulling operation such aswithdrawing partially or substantially buried objects from the ground,or for pulling cable through conduit, for example.

Derricks of this type are highly mobile, usually mounted on auto truckbodies, and are equipped with a winch. The winch in many instances ismounted at the outer end of the boom. In other models of derrick orcrane, the winch may be on the main boom column or in the bed of thetruck. In these cases, the winch line or cable is threaded through asheave at the outer end of the boom. The winches, regardless of positionrelative to the boom, generally have approximately the same line orcable pulling force. The line pulling force is independent of the angleof elevation of the derrick boom. The physical capacity of the derrickor crane boom to hold its position under load, however, varies atdifferent angles of elevation from the horizontal. This is, of course,due to the increasing bending moment on the derrick boom as the derrickboom is lowered and/or extended from a near vertical position to thehorizontal position. In unearthing objects, such as poles or stumps, forinstance, one is faced with unknown forces of resistance due to soilcondition, shape of pole, depth to which the pole is set, or, in thecase of stumps, root and soil conditions and the' like. Pulling cablethrough conduit is another example of unknown forces of resistance towhich a derrick and winch might be applied. Heretofore, if the operatorhad his choice, he would park and set his truck so that the boom endcould be positioned in close proximity to the object to be worked on,while yet at a maximum elevation to the horizontal. More often, however,the derrick must be located and set on the nearest level and firmsurface, frequently on the road, and the boom extended toward the objectto be moved, oftentimes at an angle near to the horizontal.

Generally, the elevation of the crane boom or A frame derrick iscontrolled by a closed hydraulic fluid circuit and a double acting liftcylinder or cylinders. Such hydraulic lift cylinders operate with fluidon both sides of the piston. When fluid is forced into the cylinderbelow the piston, the piston travels away from the direction in whichthe pressure is exerted upon it, while the fluid above the piston isdriven back into the fluid reservoir. On the other hand, when fluid isforced into the cylinder above the piston, the piston is forced down andthe fluid below is forced out of the cylinder back to the reservoir.When the directional control or operating valve is in neutral position,all ports are closed and the piston is locked in place by fluidentrapped on both sides of the piston. It is in this neutral positionthat the boom elevation has been heretofore maintained as the winch isoperated to apply its pulling force in tension between the object to bemoved and the end of the boom.

To avoid bending damage to the derrick or crane, particularly so in thecase of a boom having an extension or stinger, ground props or stifflegs are employed to prop the derrick or boom close to the sheave overwhich the cable is in tension. This has not always prevented damage tothe derrick when overloads occurred, as the boom lift cylinders continueto hold the load even though the stiff leg bends or may be depressedinto the ground. The overload forces are then transmitted into bendingmoment on the derrick or boom as the end of the boom attempts to followthe load and bends, the lift cylinders being locked in neutral position.

Applicant has overcome the foregoing deficiencies in present hydrauliccircuits for cranes and derricks of the rotating or A frame type byproviding a protection arrangement in the hydraulic system. The methodprovides winching while the derrick or boom is in the boom down positionagainst a stiff leg or ground support. For instance, in a pole-pullingoperation, a constant moderate down pressure is maintained on the groundprop or stiff leg by the double acting lift cylinders of the boom. Thisis accomplished by incorporating a spring loaded pressure relief valvein the line or lines between the boom down side of the directionalcontrol valve and the top side of the boom lift cylinder or cylinderstogether with a bypass line from the pressure relief valve to thereservoir. The operator then secures the operating valve in the boomdown position. The winch is engaged to place force in tension on thepole or object to be withdrawn. If these combined forces on the stiffleg or ground prop cause it to bend or sink into the ground, the boomwill automatically follow it down, avoiding an overload bending momentfrom being applied to the boom, thus saving it from damage. Location ofthe spring-loaded relief valve and bypass in the hydraulic circuit issuch that the hydraulic derricks capacity to lift and hold loads is notaffected as the spring loaded relief valve is adapted to operate only onthe boom down pressure to assure that only moderate down pressure isapplied.

It is accordingly the principal object of this invention to provide inthe hydraulic circuit of a hydraulically actuated derrick or crane,bypass means adapted and arranged to effect a safety against excessivebending moment on the boom operative on the down pressure side of thehydraulic circuit controlling the lowering of the boom.

It is another object of this invention to accomplish pulling or winchingoperations while the crane or derrick is in the boom down position andapplying moderate down pressure against a stiff leg or ground prop.

These and other objects and advantages will appear as the ensuingdescription proceeds, taken in conjunction with the accompanyingdrawings; in which:

FIG. 1 is an elevational view illustrating a derrick or crane having aboom mounted in a truck body, the boom having at its distal end a powerwinch, the cable of which is engaged adjacent the base of a pole set inthe ground. In the instance illustrated, the crane is of the rotatingtype having an extendable boom;

FIG. 2 is a partial view of the elevation cylinder of the boom of FIG.1, partly in section, together with the schematic hydraulic circuit forits operation in accordance with the present invention; and

FIG. 3 is a plan view of a conventional adjustable spring loadedpressure relief valve utilized in connection with a bypass line as asafety device in the invention described herein.

Referring in greater detail to the drawings, numeral 10 denotes a motorvehicle, the body of which has been provided with extendable legs oroutriggers l1 and 12, to maintain the truck body stable. Mounted in thetruck body is a derrick base 15. Above the base 15, in a rotatingderrick as distinguished from an A frame derrick, is mounted a turntable16, adapted for rotation with respect to the base 15, preferably on ballbearings. To the turntable 16 is mounted a frame 17, forming a clevisframe within which the end of the derrick boom 18 is pivotally mountedby a suitable shaft 19, preferably having self-aligning ball bearingbushings.

Also mounted to the clevis frame 17 between the frame and the derrickboom 18 is hydraulic boom lift cylinder 20. The boom lift cylinder 20,provided with a piston 22 and piston rod 22a, is pivotally mounted atone end to the frame at 21, and at the other end to the boom at 23. Thepivots 19, 21 and 23, together with the extensible hydraulic liftcylinder and piston, provide triangulation, so that the boom 18 can beraised or lowered through a wide range of angles from about 15 from thevertical to about 15 below horizontal.

It will be understood that, although not illustrated, for maximum safetyand stability the boom 18 is usually provided with a dual set ofhydraulic lift cylinders and pistons oppositely mounted between clevisframe 17 and the derrick boom 18.

The boom 18 may also have a telescoping extension which slides withinthe boom base 18 on suitable roller bearings and may also be providedwith a hydraulically actuated digging auger 26. The boom extension orstinger" 25 is operated in well-known manner by a hydraulic cylinder notshown. In the case of the A frame derrick, rotatability is not provided,but a boom extension may be provided.

At the outer end 27 of the boom (extension 25) is mounted a conventionalhydraulic winch, driven by a hydraulic motor not shown, all well knownin the art. Extending from the winch drum 28 mounted within the boom'end 27, is a cable 29 secured to a pole 30 by a hook 31 engaged with achain 32 secured around the pole near the ground.

A ground support or stiff leg 33 is shown extending between its groundshoe 34 and the boom end 27.

Turning to the hydraulic circuit for controlling the elevationcapabilities of the derrick, wherein lies the safety feature of theinvention, FIG. 2 shows schematically the lift cylinder 20 andassociated hydraulic circuit. It is assumed that the circuit has beenfilled with hydraulic fluid and bled of air, all lines are full, thepump primed and operating.

Pump 35, usually driven by a power takeoff from the engine of the truckon which the derrick is mounted, pumps hydraulic fluid continuously fromreservoir or tank 36 through lines 37 and 38 to an operational ordistribution valve 39. The directional valve 39 is of conventional typehaving three distributive positions. It is preferably a spool-type valvehaving an operating lever 39a for hand operation to several differentpositions. When the lever 39a is placed in the boom lift position, thedirectional control operational valve passes fluid through lines 38 and40, while permitting fluid to return through line 43, valve 44, lines 45and 46, to the reservoir 36. When the lever 39a is placed in the boomdown position, the fluid is passed through lines 38, 45 and 43, to thedistal side of the piston 22, while returns via line 40, valve 39, andline 46 to the reservoir. The third principal position of thedirectional control valve 39 is its neutral position. When the lever 39ais in this position, both the lift and down positions of valve 39 areclosed. In this position no work is done and fluid is merely circulatedby the pump through the valve 39, lines 37, 38 and 46 to and from thereservoir 36.

Assuming the directional control valve 39 is in its lift position, fluidwill flow from the tank 36, line 37, into pump 35, then through line 38,distribution valve 39, line 40, into the cylinder 20, via connection 41behind piston 22, forcing piston 22 connected to boom 18 upwardly. Thepiston 22, in turn, expels fluid in cylinder 20 ahead of piston 22through connection 42 and line 43 to valve 44. Ports 44a and 44b ofvalve 44 normally function as a through return via line 45 to the fluidreservoir 36. The valve 44 is also provided internally with aspring-loaded poppet which when open passes fluid through port 440 towhich bypass line 47 is connected, and returns hydraulic fluid to thereservoir 36.

Thus, when the derrick boom has been raised to any given elevation, theboom may be locked in place by lever 39a, placing operational valve 39in its neutral position, so that the piston 22 remains stationary withfluid pressure in cylinder 20 on each side being equal, while the pump35 continues to circulate oil from and to the'reservoir 36 through lines37, 38 and 46.

Let us assume now that the derrick boom has been extended and is beingmoved downwardly to the position shown in FIG. 1, viz, approximatelyhorizontal. The pump 35 draws fluid from reservoir 36 through line 37,then through line 38 to valve 39, which is in its down position, causingfluid to be directed through line 45, through port 440 of the pressurerelief valve 44, its through port 44b, line 43, connection 42, to

the distal side of the piston 22, thus forcing the piston 22 inwardly tolower the boom l8, lacing a modest down pressure on the stiff leg 33. Asprevious y mentioned, the valve 44 has a relief port 440, normallyclosed by stemmed valve member, not shown, urged to its closed positionby a spring bias. The tension of the spring may be adjustable, andpreferably tensioned to open at about I p.s.i.g. During the lowering ofboom 18, hydraulic fluid behind the piston 22 is returned throughconnection 41, line 40, valve 39, line 38 and pump 35 to the reservoir36. A suitable commercially available relief valve for this purpose isthe Pneu-Trol Series RV-700. The operational valve 39 is then locked inthe boom down position. As the stiff leg 33 resists the downwardmovement of the boom 18, the hydraulic pressure builds in excess of thetension of spring in pressure relief valve 44, permitting hydraulicfluid to be bypassed through line 47 to the reservoir 36. The winch 28is started, exerting tension on the base of pole 30 against and equaland opposite force in compression exerted on the boom end 27 via theground and stiff leg 33. Should the winch force in tension exceed theability of the stiff leg and/or the ground to support the compressionforce developed, and either gives way, boom 18 will follow the stiff legdown as it or the ground gives way. This allows the operator time tohalt the operation by slacking off the winch without the boom extensionhaving been bent by excess bending moment.

The operation can again be commenced when the ground support has beenreplaced or repositioned, or if beyond the capacity of the equipment,heavier duty equipment can be brought to bear.

Directional control and relief valves used in the system above describedare conventional and may be obtained commercially from a number ofsuppliers, such as Auto-Ponents, Deltrol Corporation, Bellwood,Illinois; Gresen Manufacturing Company, Minneapolis, Minnesota; orWaterman Hydraulics Corporation, Skokie, Illinois.

Having described the invention in detail, it will be apparent to thoseskilled in the art that other means may be provided to provide overloadrelief to prevent bending of the derrick boom upon overload, and allsuch means as fall within the spirit of the invention are intended tocome within the scope of the appended claims, wherein there is claimed:

I claim:

1. In a method of pulling objects against frictional forces resistingthe pulling thereof by winch, the cable of which extends from the distalend of a derrick or crane boom without damage thereto, the latter havinghydraulic circuit means including a directional control valve forcontrolling lift and lowering thereof, the steps of which includesecuring the free end of the winch cable to the object to be pulled,lowering the derrick or boom to the appropriate angle to the horizontal,and supporting the derrick or boom by placing a stiff leg or groundsupport between it and the ground, the improvement comprising providingin the boom down portion of said hydraulic circuit a valve means adaptedand arranged to bypass hydraulic fluid at a preselected pressure lessthan that pressure which will overload the derrick or boom had itsposition been locked by the directional control valve, maintaining saidpreselected pressure on the stiff leg by setting the directional controlvalve of the derrick or crane boom into boom down position, andoperating the winch to exert pulling force on the object to bewithdrawn, whereby in the event the winch pulling force is resisted bythe object being pulled to the extent that the ground or ground supportgives way, the boom follows the winch line load down without damage tothe crane boom or derrick, and provides the operator time to disengagethe winch and reposition the derrick or boom and stiff leg.

2. Method as claimed in claim 1, in which the bypass means includes apressure relief valve having a port set to open at said preselectedpressure and a bypass line to pass the fluid from said port to thesystem reservoir for recirculation so long as said port of the pressurerelief valve remains open.

1. In a method of pulling objects against frictional forces resistingthe pulling thereof by winch, the cable of which extends from the distalend of a derrick or crane boom without damage thereto, the latter havinghydraulic circuit means including a directional control valve forcontrolling lift and lowering thereof, the steps of which includesecuring the free end of the winch cable to the object to be pulled,lowering the derrick or boom to the appropriate angle to the horizontal,and supporting the derrick or boom by placing a stiff leg or groundsupport between it and the ground, the improvement comprising providingin the boom down portion of said hydraulic circuit a valve means adaptedand arranged to bypass hydraulic fluid at a preselected pressure lessthan that pressure which will overload the derrick or boom had itsposition been locked by the directional control valve, maintaining saidpreselected pressure on the stiff leg by setting the directional controlvalve of the derrick or crane boom into boom down position, andoperating the winch to exert pulling force on the object to bewithdrawn, whereby in the event the winch pulling force is resisted bythe object being pulled to the extent that the ground or ground supportgives way, the boom follows the winch line load down without damage tothe crane boom or derrick, and provides the operator time to disengagethe winch and reposition the derrick or boom and stiff leg.
 2. Method asclaimed in claim 1, in which the bypass means includes a pressure reliefvalve having a port set to open at said preselected pressure and abypass line to pass the fluid from said port to the system reservoir forrecirculation so long as said port of the pressure relief valve remainsopen.